Micro-gas sensor with a suspended micro-heater for ammonia gas detection

In this research, the ammonia micro-gas sensor is developed by micro-electromechanical systems (MEMS) technology. A suspended micro-heater is also integrated on the same chip to provide the optimal operating temperature during sensing. The main processing steps of the implemented micro-sensor in this study involve five photolithographic and seven thin-film deposition processes. In addition, in order to reduce the heat loss of the heater, this study uses anisotropic wet etching of MEMS technology to create a suspension structure that can reduce the heat conduction of silicon. Finally, tungsten trioxide is used as a sensing film to measure the variation of resistance. The chip size of the proposed micro ammonia sensor developed in this paper is 5 mm x 5 mm. At the concentration of 5 ppm ammonia, the sensing response can reach 252%, and the response time is 30 s. The lowest detection limit reaches 40 ppb. In summary, the micro-ammonia gas sensor with a micro-heater developed in this paper has the advantages of high response value, low detection limit and small size.